1. Field of the Invention
This invention relates to an electron-emitting device (a cold cathode) and a process for making the same.
2. Description of the Prior Art
In order for electrons to be emitted, an electron cold cathode is comprised of a cathode emitter whose end is worked into a needle tip so as to have a curvature of 10 .mu.m at its tip, and is so constituted that a strong electric field of about 10.sup.6 V/cm may be concentrated to the tip of this cathode emitter. Such an electron-emitting device commonly has a high current density and also does not require the heating of a cathode, and hence has the advantages that its power consumption can be very small and also it can be used as a point electron-ray source.
An electron-emitting device array is also conventionally known, which comprises a number of electron-emitting devices disposed in array. It has been also attempted to use such an electron-emitting device array in a flat panel display or the like (see Dispray, p. 37, Jan. 1987). A process for preparing a conventional electron-emitting device array will be described below with reference to the accompanying drawings.
As shown in FIG. 1, an electrical insulating substrate 101 is provided thereon with a conductive film 102, an insulating layer 103 and a conductive film 104 which are successively formed by vacuum deposition using suitable masks, and a plurality of cavities 105 disposed in array are produced. Subsequently, while a hole of each cavity 105 is gradually closed with a suitable material 107 by rotary oblique vacuum deposition, a cathode material 106 is regularly vacuum-deposited above the hole, so that a pyramidal, cathode emitter cone 108 is formed on the conductive film 102 in each cavity 105. Finally, the material 107 is removed as shown in FIG. 1B (Journal of Applied Physics, Vol. 39, p. 3504, 1968; etc.),
Another example of a process for making a conventional electron-emitting device array will be described with reference to FIGS. 2A to 2F. As shown in FIG. 2A, a plural number of electrically insulating rectangular substrates 121 are prepared, and a cathode material thin film 122 is deposited on one surface of each substrate. A plural number of substrates 123 with cathode thin films are put together to be integrated, and then each surface of the substrates thus put together, i.e., joined or combined substrates 124, is mechanically polished. Next, as shown in FIG. 2B, a metal layer 125 is formed by vacuum deposition on one broad surface of the combined substrates, and, as shown in FIG. 2C, an aperture 126 having a width substantially equal to the thickness of the cathode material thin film 122, is made in the metal layer 125 by a lithography technique, at the position right above each cathode material thin film 122. The resulting product is then separated into each substrate 123 with a cathode material thin film, and, as shown in FIG. 2D, the cathode material thin film 122 on each substrate 123 is worked by etching so as to have tips with a pattern of sharp crests. In all the substrates 123 thus obtained, the substrate 121 is partly removed by appropriate chemical corrosion to the extent that the vicinity of the tips of the cathode emitter 127 of each substrate becomes separate from the substrate 121 as shown in FIG. 2E and also the metal layer 125 with the aperture 126 projects from the substrate 121 in the form of a shelf. A cavity 128 is thus formed in each substrate 123. Then, as shown in FIG. 2F, the substrates 123 are again put together and fixed so as to be in the same state as the combined substrates 124 having been not separated. A thin-film cold cathode array can be thus obtained. (Japanese Patent Publication No. 54-17551).
However, in the process for making the former of the above conventional techniques, the rotary oblique vacuum deposition and the rotary vacuum deposition carried out from right above the hole are simultaneously performed when the cathode emitter cone 108 is formed in the cavity 105, and it is very difficult to accurately control the simultaneous vacuum deposition.
On the other hand, in the process for making the latter, an attempt to enhance the accuracy of alignment of the aperture 126 and the cathode material thin film 122 requires a high accuracy in the sheet thickness of the insulating substrate 121 and the film thickness of the cathode material thin film 122. In addition, the accuracy for integrating and fixing substrates must be identical before and after the combined substrates 124 are separated, and it is very difficult to fix them in a good accuracy.